As is well known, semiconductor device manufacture typically involves a multiplicity of steps. Many (if not all) of the steps, if not carried out according to specification, can result in devices that do not pass final inspection, or that fall during life testing. It is obviously expensive, and thus highly undesirable, to have to substantially complete device manufacture and then to subject all, or at least a representative sample, of the devices to a life test in order to ascertain the adequacy of some intermediate manufacturing step. Thus, it would be highly desirable to have available an inspection technique that could be used, inter alia, to pre-screen devices, and to identify potentially unreliable devices. This application discloses such a technique, discloses a manufacturing process that comprises an inspection step that involves use of the technique, and also discloses apparatus that can be used to practice the technique.
Although the apparatus and technique are advantageously employed in semiconductor device manufacturing, theft use is not thus limited. In particular, the apparatus and technique can also advantageously be used in the development of new semiconductor device designs and/or of semiconductor device manufacturing methods, as those skilled in the art will recognize. It can also be used to test packaged devices.
Thermal imaging of semiconductor devices is known. See, for instance, R. J. Stetson, et al., Laser Focus World, June 1990. As stated in that article, non-contact temperature measurements can be made ". . . with a spatial resolution as small as 15 .mu.m." The article further discloses that the prior art IR imaging method utilizes scanning, with the scanning rate being on the order of microseconds/point.
These capabilities, although adequate for some purposes, are inadequate for other purposes. In particular, it would be desirable for many purposes (exemplarily including semiconductor laser fabrication) to have available thermal imaging means capable of providing a substantially diffraction-limited thermal image of a body (exemplarily in the approximate wavelength range 3-5 .mu.m). It would also be deskable if the high resolution thermal imaging means could form an image at a given moment in time (i.e., provide a "snapshot" of the temperature distribution at a given moment in time). The former capability could, for instance, be used to pin-point the location and cause of hot spots in semiconductor lasers, and to assess the uniformity of the heat sinking or of the laser, and the latter could be used to, e.g., reveal transient thermal states. This application discloses thermal imaging means that can provide these capabilities.